An off-line power supply receives power from an alternating-current (AC) source and provides a voltage-regulated, direct-current (DC) output that can be used to power a load. An exemplary off-line power supply includes a power factor correction (PFC) stage and a DC-to-DC converter stage. The PFC stage receives the AC input signal, performs rectification and maintains current drawn from the AC source substantially in phase with the AC voltage so that the power supply appears as a resistive load to the AC source. The DC-to-DC converter stage receives the rectified output of the PFC stage and generates the voltage-regulated, DC output which can be used to power the load. The rectified output of the PFC stage is typically at higher voltage and is more loosely regulated than the output of the DC-to-DC stage.
An exemplary DC-to-DC converter includes a series resonant circuit (SRC) topology. In this configuration, an inductor and a capacitor are connected in series to form a resonant tank. A switching inverter charges the resonant tank with energy. A load receives power from the resonant tank. Adjusting the switching frequency of the inverter changes the impedance of the resonant tank, and because the resonant tank is in series with the load, this changes the power delivered to the load. The switching frequency can be adjusted to maintain the DC output voltage constant.
It is desired to provide an improved off-line power supply.